1. Field of the Invention
The present invention relates to a laser fixing device, an image forming apparatus equipped with the laser fixing device, and an image forming method employing the image forming apparatus.
2. Description of the Related Art
An electrophotographic image forming apparatus (such for example as a printer) is equipped with a fixing device for fixing an image onto a recording sheet. The fixing device causes a toner constituting a toner image formed on a recording sheet to melt, thereby fixing the toner image onto the recording sheet.
As an example of such a fixing device, there is known a fixing device of heat-roller fixing type comprising a fixing roller and a pressure section, such as described in Japanese Unexamined Patent Publication JP-A 11-38802 (1999). In this heat-roller type fixing device, a recording sheet bearing a yet-to-be-fixed toner image is sandwiched between the fixing roller having a heating portion thereinside and the pressure section which is brought into pressure-contact with the fixing roller. In this way, the toner borne on the recording sheet is fused on the recording sheet.
In such a heat-roller type fixing device, the surface temperature of the fixing roller needs to be raised to a predetermined level by the heating portion to fuse the toner under application of heat. Therefore image formation cannot be effected immediately upon start-up of the apparatus, and a certain amount of time is required to be ready for image formation. Furthermore, when it is desired to keep the surface of the fixing roller at a predetermined temperature for immediate image formation, the surface of the fixing roller needs to be heated continuously, which results in an increase in energy consumption.
In view of the foregoing, as a fixing device capable of fixing toner images without spending much time while suppressing an increase in energy consumption, there is proposed an optical fixing device for fusing and fixing a toner by exploiting optical energy.
In Japanese Unexamined Patent Publication JP-A 7-191560 (1995), as an optical fixing device, there is shown a laser fixing device having an array of a plurality of laser light emitting devices for applying laser light to a toner. According to the laser fixing device described in JP-A 7-191560, in contrast to a laser fixing device having a single laser light emitting device only, there is no need to cause laser light reflection by means of a polygon mirror or otherwise. It will thus be seen that the laser fixing device can be made compact.
In addition, in Japanese Unexamined Patent Publication JP-A 2005-115194, as an optical fixing device, there is shown a flash fixing device for fusing a toner by means of flash light having wavelengths ranging from 800 nm to 1000 nm. In JP-A 2005-115194, as a light fixable toner, there is shown an infrared-fixable toner containing an infrared absorbing agent having an absorption peak wavelength within a range of from 800 nm to 1000 nm in terms of light absorption characteristics.
Examples of the light fixable toner includes, in addition to the infrared-fixable toner, a visible light-fixable toner configured to be fused and fixed by visible light and an ultraviolet-fixable toner configured to be fused and fixed by ultraviolet light. These light fixable toners differ from one another not only in light absorption characteristic but also in the quality of obtained images. For example, given that an image is formed by using the infrared-fixable toner, since the infrared absorbing agent even absorbs visible light in a range near the infrared region, it follows that the obtained image suffers a decline in color reproducibility in its red-color area. It is therefore desirable to select a light fixable toner for use appropriately according to purposes.
What must be necessary for appropriate use of a light fixable toner as the situation demands is an optical fixing device and an image forming apparatus as well adapted to use of a plurality of types of light fixable toners having different light absorption characteristics. In this respect, there is a problem in the optical fixing devices disclosed in JP-A 7-191560 and JP-A 2005-115194 in that these optical fixing devices are designed to deal with only one light fixable toner.